Spark plug with a conductive glass seal electrode of glass, copper and zinc



Oct. 24, 1967 J. E. BLUM ETAL 3,

. SPARK PLUG WITH A- CONDUCTIVE GLASS SEAL ELECTRODE OF GLASS, COPPER AND ZINC Filed June 16. 1966 INVENTOR. 04 155/1122? 5 BY 17765 [1/ ze// Ju/QZ ram/0 United States Patent SPARK PLUG WITH A CONDUCTIV E GLASS SEAL ELECTRODE 0F GLASS, COPPER AND ZINC Jack E. Blum and James W. Ezell, Flint, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed June 16, 1966, Ser. No. 563,324 9 Claims. (Cl. 313-136) This invention relates to an improved ceramic-to-metal conductive glass seal for spark plugs and the like.

It is common practice in the spark plug art to form a part of the center electrode conductive path which extends through the insulator of a fused mass of glass and conductive material which bonds to the ceramic, the center electrode and the terminal screw, thereby forming an electrically conductive hermetic seal. Such seals are shown, for example, by United States Patents 2,106,578, issued to Karl Schwartzwalder and William Shuford Kirk, and 2,248,415, issued to Karl Schwartzwalder and Alexander S. Rulka. The latter patent discloses a seal consisting of about 50% copper powder and 50% glass. The composition which is presently most commonly used for conductive glass seals in high production automotive-type spark plugs consists of about 58% copper and 42% glass. In practice a seal of this type is formed by first positioning the metal center electrode in the lower part of the insulator centerbore, injecting into the centerbore over the top of the center electrode a charge of the metal-glass seal mixture in powder form, inserting a metal terminal screw into the centerbore and then heating so as to cause the glass seal mixture to soften while simultaneously pressing down on the terminal screw. In this manner pressure is applied to the softened glass material to cause it to densify and to bond to the insulator, the center electrode and the terminal screw. It has been found that the application of pressure to the seal while it is in the softened condition is essential for the reasons indicated, i.e., to assure non-porosity and good bonding. However, by reason of such pressure having been applied, the finished hardened seal is in something of a stressed condition and if the seal is reheated to a certain temperature, it will rapidly expand and lose its sealing properties. The temperatures to which the seal, must be reheated to create such conditions is referred to as the backup temperature and is, of course, characteristic of the particular seal composition used. The fact is, however,

that for all glass sealing compositions heretofore known,

for example those shown in the aforementioned prior patents, the backup temperature is very much lower than the temperature to which the sealing material must be initially heated in order to cause softening during manufacture. As a typical example, the sealing material mixture consisting of 58% copper powder and 42% borosilicate glass powder presently in common use requires heating to 1500-1600 F. to cause softening .during processing, and

the seal so formed hasa backup temperature of 1250. to 1350 F. This can be a problemsince under severe operating conditions or improver plug installation, the temperature at the location of the seal can reach a temperature higher than 1350' F. thereby causing a permanent failure of the sealfiIt is a relatively simple matter, of course, to formulate a seal composition with a somewhat higher initial softening temperature and with a commensurately somewhat higher backup temperature. However,

it is not a satisfactory solution to the problem for the .reason that the metal parts involved cannot tolerate processing temperatures much in excess of 1700 F. and it would be prohibitively expensive to make such parts of a more resistant metal. v.

It is a primary object of this invention to provide a hermetic conductive glass seal which is operative at tem- 3,349,275 Patented Oct. 24, 1967 peratures up to 1650 F. without initially heating the seal mixture above 1600 F. It is another object of this invention to provide a seal which is operative at temperatures up to 1650 F. which can be formed at low cost utilizing standard spark plug manufacturing techniques.

These and other objects are accomplished by a metalglass sealing material mixture containing zinc or manganese. The composition of the conductive metal-glass seal consists essentially of 40 to 60 weight percent copper powder, 25 to 35 weight percent glass and 10 to 30 weight percent zinc or manganese. When a spark plug containing the composition described above is heated and pressed with a terminal screw at a seal temperature of between 1500 and 1600 F., the resulting fused mass forms a hermetic conductive glass seal which is durable and operative up to a temperature of at least 1650 F., a temperature which is seldom exceeded at seal location during spark plug operation even under severe operating conditions.

Other objects and advantages of this invention will be apparent from the following detailed description, reference being made to the accompanying drawing wherein a preferred embodiment of this invention is shown.

Referring now to the drawing, the spark plug 10 comprises a conventional outer metal shell 12 having a ground electrode 14 welded to the lower end thereof. Positioned within the metal shell 12 and secured in the conventional manner is an insulator 16. The ceramic insulator 16 should preferably be of a high alumina base material containing upwards of aluminum oxide such, for example, as covered by United States Patent 2,760,875 issued to Karl Schwartzwalder and Helen Blair Barlett. Such an insulator has excellent mechanical strength and heat shock resistance along with the ability to form an excellent bond with glass, all these characteristics being of considerable advantage in forming the conductive seal of this invention. The insulator 16 is formed with a centerbore having a lower portion 18 of relatively small diameter, and an upper portion 20 of larger diameter which are connected by insulator centerb-ore ledge 26. Positioned in the lower portion 18 of the insulator centerbore is the center electrode 22. The center electrode 22 has an enlarged head 24 at the upper end thereof which rests on the insulator centerbore ledge 26 and a serrated lower end 28 thereof projecting beyond the lower tip of the insulator 16. Positioned in the upper portion 20 of the insulator centerbore is the terminal screw 32. A metal-glass seal 30 forms a hermetic conductive seal in the insulator centerbore portion 20. The conductive metal-glass seal 30 is bonded to the center electrode head'24, the terminal screw 32 and the inner walls of the ceramic insulator to provide an electrically conductive path from the terminal screw 32 to the center electrode 22 and to provide a hermetic seal in the insulator centerbore portion 20.

In accordance with the present invention the metalglass seal 30 is a dense, fused mass of copper, zinc or manganese and glass consisting essentially of 40 to 60 weight percent copper, 10 to 30 weight percent zinc or manganese and 25 to 35 weight percent glass. The concentration of copper should be 40 to 60 weight percent in order to obtain a seal with a resistance of less than one ohm, the resistance commonly used in spark plug seal systems.

The presence of 10 to 30 weight percent of a metal taken from the group consisting of zinc and manganese in the metal-glass seal composition enables the glass seal to have a higher backup temperature, for example in the range of 1650 to 1750" F. Zinc concentrations of less than 10% have little effect on the high temperature stability of the seal. Seals having zinc concentrations greater than 30% form excessive amounts of copper-zinc alloy which tends to ext-rude at elevated temperatures thereby causing the seal to leak during actual engine operation. The preferred zinc concentration is 15 to 20 weight percent. The manganese concentration range is 10 to 30 weight percent and the preferred concentration range is 15 to 20 weight percent.

We are unable to completely describe the theory or reasons why the presence of Zinc or manganese causes the unexpected increase in the backup temperature of the metal-glass seal. It has been observed that when zinc or manganese is intimately blended with glass and heated to a temperature between 1500 and 1600 F. to form the seal, a volatile constituent is released from the glass. The removal of this volatile constituent eliminates subsequent gas evolution which normally occurs upon reheating the seal to a temperature of 1300 F. or higher. This gas evolution that normally occurs upon reheating contributes to a seal having a low backup temperature. It has also been observed that zinc and manganese apparently alloy to some extent with copper to form a copper-zinc or copper-manganese alloy which at low concentrations apparently contributes to a high backup temperature.

The glass in the metal-glass seal is the conventional borosilicate-type glass commonly known as Pyrex, which is presently being used in the production of automotive spark plugs. The composition of a preferred borosilicate glass is 65% by weight SiO 23% by weight B by weight A1 0 and 7% by weight Na O. This glass will be hereafter referred to as glass A. Other glass frit compositions may be used in the seal as long as they soften at a temperature between 1560 and 1600 F. The concentration of the glass in the metal-glass seal is not critical. This preferred glass concentration range is from about 25 to 35 weight percent. The mesh size of the glass powder does not appreciably affect the performance of the seal, a mesh size of 200 for the glass powder was found to be satisfactory.

Another component which may be added if desired in the metal-glass seal composition is a binder. A small amount of organic binder such as hydrogenated cottonseed oil may be admixed with the powder and the mixture then compressed into a self-sustaining pellet which will serve as a convenient manner of inserting the desired amount of powdered mixture into the insulator centerbore. The organic binder, of course, decomposes and goes off as a gas during the heating and pressing opera tion. The amount of binder in the mixture ranges from 1 to 3%. Other binders which may be used are carboxyl methyl cellulose, 1201 wax, dextrin, and the like.

A preferred embodiment of the present invention is a glass seal mixture having a composition of 50 weight percent copper powder, 20 weight percent zinc and 30 weight percent glass A. This metal-glass powder mixture is mixed with 1 part hydrogenated cottonseed oil, wetted with a dextrin solution and then placed in the insulator centerbore and tamped. The metal terminal screw is then placed into the centerbore and the glass seal mixture heated to a temperature of 1500 F. to 1600 F. As the glass seal mixture is softened, the terminal screw is pressed down into the soft glass seal mixture. Upon cooling, a hermetic conductive seal is formed. This seal has to be reheated to a temperature above 1650 F. before it loses its scaling properties; that is, the backup temperature of this seal is higher than 1650" F. As mentioned earlier, the backup temperature of a typical metal-glass seal presently being used in automotive spark plugs containing 58% copper and 42% borosilicate glass is of the order of 1300" F.

Another embodiment of this invention is a glass seal composition containing 60 weight percent copper powder, 10 weight percent manganese powder and 30 weight percent glass. The conductive metal-glass seal formed from this seal mixture composition has a backup temperature in the range of1650 F. to 1700 F.

While the invention has been described in terms of a preferred embodiment, it is to be understood that it is not limited thereby except as defined in the following claims.

What is claimed is:

1. An electrically conductive hermetic seal adapted to operate at elevated temperatures in a ceramic insulator containing copper, glass and a metal taken from the group consisting of zinc and manganese.

2. An electrical conductive hermetic seal adapted to operate at temperatures up to 1650 F. in a ceramic insulator consisting essentially of 40 to 60 weight percent copper, 10 to 30 weight percent of a metal taken from the group consisting of Zinc and manganese and 25 to 35 weight percent glass.

3. A seal as described in claim 2 wherein said seal contains 15 to 20 weight percent zinc.

4. A sealing composition for forming an electrical conductive hermetic seal in a ceramic insulator at temperatures of 1600 F. or below, said seal adapted to operate at temperatures up to 1650 F., said sealing composition containing 40 to 60 parts by weight copper powder, 10 to 30 parts by weight of a metal taken from the group consisting of zinc and manganese and 25 to 35 parts by weight glass.

5. A sealing composition for forming an electrically conductive hermetic seal in a ceramic insulator at a temperature of 1600 F. or below, said seal adapted to operate hermetically at temperatures up to 1650 B, said sealing composition containing about 48 to 52 parts by weight copper powder, about 15 to 20 parts by weight zinc and about 28 to 32 parts by weight glass.

6. A spark plug comprising a ceramic insulator having a centerbore therethrough, a metal member in said center'bore and a dense, fused, electrically conductive mass bonded to said metal member and bonded to said ceramic insulator to form a hermetic seal in said centerbore, said hermetic seal adapted to operate hermetically at temperatures up to 1650 F., said mass consisting essentially of 40 to 60 weight percent copper powder, 10 to 30 weight percent of a metal taken from the group consisting of zinc and manganese and 25 to 35 weight percent glass.

7. A spark plug as described in claim 6 wherein said mass consists of 48 to 52 weight percent copper, 15 to 20 weight percent zinc and 28 to 32 weight percent glass.

8. A sealing composition for forming an electrical conductive hermetic seal at temperatures of 1600 F. or below, said seal adapted to operate at temperatures up to 1650 F., said sealing composition containing 40 to 60 parts by weight copper powder, 10 to 30 parts by weight of a metal taken from the group consisting of zinc and manganese and 25 to 35 parts by weight glass.

9. A spark plug comprising a ceramic insulator having a centerbore therethrough, a center electrode in said centerbore, a terminal screw in said centerbore in spaced relation to said center electrode, and a dense, fused, electrically conductive mass positioned in said centerbore bonded to said terminal screw and said center electrode and to said ceramic insulator to form a hermetic conductive seal in said centerbore, said hermetic seal adapted to operate hermetically at temperatures up to 1650 F., said mass consisting essentially of 40 to 60 weight percent copper powder, 10 to 30 weight percent of a metal taken from the group consisting of zinc and manganese and 25 to 35 weight percent glass.

References Cited UNITED STATES PATENTS 2,837,679 6/ 1958 Schwartzwalder et al. 313-136 2,988,662 6/1961 Smith 313-191 3,247,132 4/1966 Schurecht 313-136 JAMES W. LAWRENCE, Primary Examiner.

C. R, CAMPBELL, J 11,, Assistant Examiner. 

9. A SPARK PLUG COMPRISING A CERAMIC INSULATOR HAVING A CENTERBORE THERETHROUGH, A CENTER ELECTRODE IN SAID CENTERBORE, A TERMINAL SCREW IN SAID CENTERBORE IN SPACED RELATION TO SAID CENTER ELECTRODE, AND A DENSE, FUSED, ELECTRICALLY CONDUCTIVE MASS POSITIONED IN SAID CENTERBORE BONDED TO SAID TERMINAL SCREW AND SAID CENTER ELECTRODE AND TO SAID CERAMIC INSULATOR TO FORM A HERMETIC CONDUCTIVE SEAL IN SAID CENTERBORE, SAID HERMETIC SEAL ADAPTED TO OPERATE HERMETICALLY AT TEMPERATURE UP TO 1650* F., SAID MASS CONSISTING ESSENTIALLY OF 40 TO 60 WEIGHT PERCENT COPPER POWDER, 10 TO 30 WEIGHT PERCENT OF A METAL TAKEN FROM THE GROUP CONSISTING OF ZINC AND MANAGANESE AND 25 TO 35 WEIGHT PERCENT GLASS. 